The invention relates in general to a gas-burner system with a radiant tube known as xe2x80x9cglove fingerxe2x80x9d, permitting the burned gases to be discharged at very high rate.
More precisely, the invention relates to a radiant device with gas burner and recirculation of burned gases for heating a vessel bounded by a wall, this device comprising in longitudinal axial direction a section external to the vessel and a section both internal to the vessel and divided into three internal subsections disposed successively at increasing distance from the wall and, in inward radial direction, an envelope comprising an external casing and an internal envelope tube, the end of which remote from the wall is closed, an exchanger disposed in the envelope and extending over a portion of the external section and over the first two internal sections, a recirculation tube extending over the third internal section at a radial distance from the envelope tube and having open inlet and outlet ends respectively relatively close to and relatively far from the wall of the vessel, a retaining tube internal to the exchanger and extending over a portion of the external section and over the first internal section, a furnace tube disposed in the exchanger, retained by the retaining tube in the extension thereof and extending over the second internal section, and a central injection tube transporting the gas, extending at least into the retaining tube and traversing a partition separating the retaining tube from the furnace tube, the exchanger comprising a separating tube that defines with the retaining tube and the furnace tube an air intake path starting in an intake inlet drilled in the casing and ending at intake orifices drilled in the furnace tube, the separating tube defining with the envelope a smoke-exhaust path ending at an exhaust outlet drilled in the casing, and the furnace tube ending in a nozzle disposed facing the inlet end of the recirculation tube.
A device of this type is known in the prior art, as illustrated in particular by French patents 2616518 and 2616520 and used with success for many years.
Precisely because the design of these devices is so relatively old, it was necessary that they be subjected to a new study, justified by the constant desire to reduce the emissions of nitrogen oxides, whose formation conditions are better known today that in the past.
Nevertheless, inasmuch as these devices have a long service life and were installed in large numbers, the design of new devices with reduced emission of nitrogen oxides also had to solve the problem posed by rehabilitation of old devices.
As it happens, this context excludes in practice recourse to the known solutions for reduction of the emissions of nitrogen oxides, either by providing a movable injector as described in, for example, German Patent 4420140, or in providing means for physically displacing the combustion zone, as described in, for example, U.S. Pat. No. 5,570,679.
Under these conditions, the objective of the invention is therefore to propose a device which on the one hand emits only a negligible level of nitrogen oxides and on the other hand differs from a known device only by entirely minor adaptations of structural nature.
To this end, the device of the invention, which furthermore is in conformity with the generic definition given in the foregoing preamble, is essentially characterized in that the central injection tube is fed by two conduits, the first of which transports at least gas and the second of which transports at least air, in that the central injection tube ends at a burner disposed in the furnace tube and discharging at the level of the nozzle, and in that a valve is interposed in at least one of the conduits, outside the casing.
According to one possible embodiment of tile invention, the first conduit, for example, transports gas and the second conduit transports air, the central injection tube then being composed of a single injection blowpipe in which the first and second conduits discharge.
In this case, it is advisable at least that the aforementioned valve be interposed in the second conduit, to control the air flowrate.
According to another possible embodiment of the invention, the first conduit, for example, transports gas and the second conduit transports a mixture of air and gas, the central injection tube then being composed of two concentric injection blowpipes in which the first and second conduits discharge respectively.
In this case it is advisable at least that the aforementioned valve be interposed on the first conduit, to control the gas flowrate.